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hatrack

(59,439 posts)
Sat Sep 12, 2020, 09:40 AM Sep 2020

Fires In NW Oregon Raging Through Areas That Normally Burn Once Every Few Centuries

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The Medford Estates neighborhood of Medford, Ore., in ruins on Thursday.Credit...Adrees Latif/Reuters

Fires are common in the east, which is normally dry, according to Philip Mote, a climate scientist at Oregon State University. In some areas of eastern Oregon the “return period,” or length of time between major fires, is as little as 20 years, he said. But the western slope of the Cascades, which catches most of the moisture that blows in from the Pacific Ocean, is normally wetter. “Out here, the return period can be hundreds of years,” he said. That protective moisture has faded, in large part because climate change has altered precipitation and temperature patterns.

Tim Brown, director of the Western Regional Climate Center at the Desert Research Institute in Reno, Nev., said the extreme warmth had caused vegetation to become exceptionally dry and to burn more readily. Temperature, humidity, wind and solar radiation combine to dry out brush and are the key elements for fire. “We call it evaporative demand,” he said. And in recent weeks, he added, “the west Cascades have been really dry from the evaporative demand.” Those dry conditions were most likely exacerbated by climate change, according to Meg Krawchuk, a professor at Oregon State’s College of Forestry. And they had the effect of “teeing up the landscape” for a wildfire, she said.

The critical moment came Monday and Tuesday, when a windstorm carried hot air from the high desert in the eastern part of Oregon over the mountains, rapidly spreading the fires in the more populated western part of the state, according to Josh Clark, fire meteorologist at the Washington State Department of Natural Resources. Those winds were the strongest the state has seen in at least 30 years, Mr. Clark said. And when they crossed the mountains, the winds raced down through river canyons, which compressed the air, warming it further and pushing it westward like a bellows.

As those fires raced west, they met unusually dry conditions, said Dr. Kolden, which in turn allowed the fires that were already burning to spread rapidly. “The fire’s able to move very quickly and just explode down these canyons,” she said.

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https://www.nytimes.com/2020/09/12/climate/oregon-wildfires.html

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